Doped C₆₀ Molecules

The molecular manipulation capabilities of the STM can be used to reversibly add dopants to a single C₆₀ molecule. This is achieved by moving individual C₆₀ molecule over K atoms stuck on the Ag(001). Due a strong attaction between K and C₆₀, the K atoms stick to the C₆₀ molecule and follow it along during further manipulations. As the movie in figure 1 shows, several K atoms can be attached using this technique.

Figure 1. Click on the picture to see a movie showing the formation of K₄C₆₀. QuickTime required

Due to large electronegativity difference between K and C₆₀, the attached K atoms transfer some of their charge to the C₆₀, making the C₆₀ molecule more negative. The degree of electron transfer can be estimated using scanning tunneling spectroscopy. Figure 2 shows STS spectra taken on K_xC₆₀ molecules during various stages of doping.

Figure 2. Spatially averaged STS spectra of K_xC₆₀ molecules taken on the molecules shown in Figure 1.

The shifts observed in the C₆₀ molecular states are consistent with a charge transfer of ~0.6 electrons being added to the C₆₀ molecule for each added K.

Please see the reference below for more information on this technique.

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References

Controlled atomic doping of a single C₆₀ molecule
R. Yamachika, M. Grobis, A. Wachowiak, and M. F. Crommie
Science 304, 281 (2004) Published online 11 March 2004 (10.1126/science.1095069)